Knowledge Organiser
Part of Reflex Arc · GCSE GCSE Biology revision
This topic summary covers Knowledge Organiser within Reflex Arc for GCSE Biology. Topic 3: Reflex Arc It is section 13 of 14 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 13 of 14
Practice
15 questions
Recall
20 flashcards
Knowledge Organiser
Key Terms
- Reflex arc — receptor → sensory → relay → motor → effector
- Involuntary — automatic; no conscious control
- Relay neurone — in spinal cord; connects sensory to motor
- Synapse — gap between neurones; neurotransmitter crosses it
- Neurotransmitter — chemical that bridges the synapse
Must-Know Facts
- Reflex arc: receptor → sensory neurone → relay neurone (spinal cord) → motor neurone → effector
- Reflexes are faster than voluntary responses because the spinal cord (not brain) coordinates the response
- Reflexes are involuntary — they occur automatically, without conscious decision; the person becomes aware through the brain shortly after but cannot prevent the reflex
- Two synapses in a typical spinal reflex: sensory-relay and relay-motor junctions
- Synapses are directional — neurotransmitters released pre-synaptically, bind post-synaptically only
- Examples: withdrawal from pain, knee-jerk reflex, pupil constriction, blinking
- Reflex purpose: protect the body from damage before the brain can process the stimulus
Common Mistakes
- Missing the relay neurone from the pathway: Many students write "receptor → sensory neurone → motor neurone → effector" — the relay neurone in the spinal cord is a required component and its omission loses a mark.
- Saying "the pathway is shorter" without explaining why: For full marks, state that the impulse is coordinated in the spinal cord rather than travelling to the brain first, reducing the total distance and therefore the response time.
- Forgetting that synapses ensure one-directional transmission: Neurotransmitter vesicles are only present on the pre-synaptic side — this is why impulses travel sensory → relay → motor, never in reverse.
- Saying reflexes happen "without the person knowing": The person becomes aware of the reflex shortly after through the brain — but they cannot prevent or consciously control it. Use the word "involuntary" rather than "without knowing."
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Practice Questions for Reflex Arc
Which word best describes a reflex action?
State the correct order of the reflex arc pathway from stimulus to response. Name each component.
Quick Recall Flashcards
15 questions on Reflex Arc — practise free
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